1. Field of the Invention
The present invention relates to an imaging apparatus equipped with an anti-shake (image shake correction/image stabilizing/shake reduction) system.
2. Description of the Related Art
Imaging apparatuses of recent years usually incorporate an anti-shake (image shake correction/image stabilizing/shake reduction) system for reduction of image shake caused by vibrations such as hand shake. Typical anti-shake systems detect vibrations applied to the imaging apparatus and/or variations in the orientation thereof, and shift an anti-shake optical element such as at least part (e.g., a lens group) of an imaging optical system or an image sensor relative to the optical axis (i.e., move the anti-shake optical element in a plane orthogonal to the optical axis) or tilt the anti-shake optical element relative to the optical axis so as to cancel out the effect of the vibrations and the orientation variations.
Voice coil motors or the like which are superior in responsiveness are used as actuators (anti-shake drive actuators) in an anti-shake driving operation of the anti-shake optical element. Voice coil motors for use in an anti-shake driving operation in imaging apparatuses include: a magnet(s) which is mounted to one of a movable member and a stationary member that movably supports the movable member; and a coil(s) which is mounted to the other of the movable member and the stationary member to be positioned within the magnetic field of the magnet. The movable member holds the anti-shake optical element that moves during an anti-shake (image-stabilizing) operation, and the movable member is driven to reduce image shake by electromagnetic force generated by the passage of electric current through the coil.
The anti-shake drive actuators need to be installed at positions that do not interrupt the optical path of the imaging optical system; in order to satisfy this requirement, a structure in which the anti-shake drive actuators are disposed outside the optical path in different radial directions from an optical axis of the imaging optical system (disclosed in Japanese Unexamined Patent Publication No. 2012-177755 (Patent Literature 1), Japanese Patent Publication No. 5,096,496 (Patent Literature 2) and Japanese Unexamined Patent Publication No. 2008-70770 (Patent Literature 3)) and a structure in which the anti-shake drive actuators are disposed on an extension of the optical path (disclosed in Japanese Unexamined Patent Publication No. 2013-246414 (Patent Literature 4)) have been proposed.
In recent years, due to increased diversification of the use of imaging apparatuses, it has been required to improve improve the operation specifications (driving amount, driving speed and flexibility in driving direction) of the anti-shake optical element. For instance, the anti-shake optical element is shifted (moved) in a plane orthogonal to an optical axis in the anti-shake system disclosed in Patent Literature 1, whereas the anti-shake optical element is made to perform a rolling operation in which the anti-shake optical element is driven to roll (rotate about the optical axis thereof) in Patent Literature 3. Furthermore, in Patent Literatures 2 and 4, movement of the anti-shake optical element is complicated; namely, a triaxial drive type anti-shake system which makes the anti-shake optical element perform the aforementioned rolling operation in addition to a tilting operation in which the anti-shake optical element is driven to produce motion including components in the pitching and yawing directions has been proposed. In this triaxial drive type anti-shake system, it is difficult to achieve a compact and powerful actuator(s) or an actuator(s) which has superior weight balance and a small load during operation.
In the case where a voice coil motor is used as an anti-shake drive actuator, if the gap (distance) between each magnet and the associated coil varies greatly during anti-shake driving operation, it is difficult to obtain a stable thrust force, which makes the anti-shake driving operation difficult to control. In addition, if the gap between each magnetic sensor which detects the state of anti-shake driving operation (variations of the magnetic field) and the associated magnet varies greatly, a great influence is exerted on the sensitivity of the magnetic sensor. As a result, it may be required to use powerful and large-size magnet(s) and coil(s), and/or the degree of difficulty in control of the anti-shake driving operation may increase. Accordingly, in the case where the anti-shake drive actuator(s) of an anti-shake system is a voice coil motor(s), there has conventionally been the challenging task of reducing such gap variations as much as possible.